Hydroelectric energy is one source of so-called renewable energy. About 48% or almost half of all electric energy is produced by steam generation using coal. Natural gas provides about 18% of U.S. electric energy, and nuclear energy now provides about 22% via steam generation. Petroleum, such as oil, is used to produce only about 1% of U.S. electric energy. Coal, natural gas and petroleum are carbon-based and when burned produce emissions which can be costly to mitigate or, if not mitigated, can be dangerous or at least increase the so-called carbon footprint in the earth's atmosphere. The supply of coal, gas and petroleum is also limited. Nuclear energy generation, unless handled with extreme care, is dangerous, and the spent nuclear fuel becomes a hazard to the world.
Consequently, the hope of electrical energy generation for the future is in so-called renewables which include, but are not limited to, the air (wind power), the sun (solar power) and water (hydroelectric and marine hydrokinetic energy) sources. The great Coulee dam, Hoover dam and the Tennessee Valley Authority are exemplary of projects started in the early 20th century in the United States. Large hydro-electric generators in such dams on rivers in the United States are now being replaced with more efficient and larger capacity generators. But the number and utility of dam-based hydroelectric power is limited, and the dams block migrating fish and commercial river traffic on navigable rivers. The dam backs up a river to form a lake which can take away valuable land resources that could be used to grow food or permit animals to feed. On the other hand, the created lakes provide water control and recreational use for boating, fishing and the like. Nevertheless, there remains a need for a device that may save the cost of building a dam, permit the marine hydrokinetic generation of electricity and use the inherent flow of a river or the flow of ocean currents, tides and waves.
So-called biomass energy generated from plant and animal material (waste) may amount to approximately 6% of total renewable energy but has similar problems to those of non-renewable carbon-based systems and can cause emissions. While hydro-electric energy amounts to the next greatest renewable source at about 4%, it is believed that more can be done to efficiently utilize the rivers, tides and ocean currents in the United States and near its shores than by hindering the flow of water commerce by the construction of dams.
Other renewable sources include geothermal, wind and solar energy. While these are “clean” sources, to date, their growth has been unimpressive. Only wind energy is supported by the Department of Energy, and wind energy is forecast to grow from 0.55 to 20% of all US energy in approximately 20 years.
Further detail of a conventional turbine is described in WO 1992/14298 published Aug. 20, 1992 and assigned to U.S. Windpower, Inc. A variable speed rotor may turn a gearbox to increase the rotational velocity output of the rotor and blade assembly. For example, a so-called cut-in speed (rotational velocity) of a rotor, for example, may be about six revolutions per minute (when electricity may be generated) and the rotor blade may typically cut-out at about 30 revolutions per minute (a maximum for electricity generation without damage to the turbine) by controlling the pitch of the rotor via a pitch control system during conditions of high wind velocity and to reduce rotor blade noise. Typically, wind speeds over 3 meters/sec are required to cause the large rotor blades to turn at the cut-in speed (rotational velocity). Wind frequency between cut-in and cut-out speeds (velocities) has been measured to vary depending on location, weather patterns and the like. Placement high on a hill or a mountain of a wind turbine, for example, may be preferable to locating the wind turbine at a low point in a valley. Consequently, it may be recognized that there are periods of time when wind turbines do not have sufficient wind speed to operate at all depending on weather conditions, placement and the like.
When wind speed reaches an excess amount, a pitch (and yaw) control system may measure the wind speed and adjust the pitch of rotor blades to pass more wind and so control the rotor blade from turning too fast as well as point the rotor blade into the wind. Yaw control may supplement pitch control to assist in pointing a rotor into the direction of wind flow. Noise from rapid rotor velocity can be abated, for example, by turning the blade parallel to the wind using a wind speed control system to thus maintain the rotational velocity close to a cut-out speed. An anemometer placed at the tail of the known wind turbine may measure wind velocity and provide a control input. The tail of the turbine may be equipped with a rudder or wind vane for pitch or yaw control. Horizontal or vertical stabilizers may be provided for pitch or yaw control. The rudder or wind vane may help point the variable speed rotor into the wind. In general, however, there is a problem with known wind turbine systems that only a portion of the wind energy available at a site of a wind turbine farm may be harnessed resulting in harnessing only a portion of the kinetic energy of the available wind to feed an electric power grid.
Also, a gearbox is known to have a failure rate of approximately 5%. Electronics used in a wind turbine has the highest potential failure rate of 26%. Control units generally exhibit a failure rate of 11%. Sensors and yaw control exhibit approximately a 10% failure rate. The failure rate of a variable frequency converter may be on the order of 26% (electronics) according to an ongoing consortium's study of drive train dynamics at the University of Strathclyde, Glasgow, Scotland. According to published information, the mean time between failures of a 1.5 megawatt wind turbine, for example, may be only two years on average (but the real failure rate is an industrial secret); and the replacement cost may be over $50,000 (for example, $50,000 to $100,000 US) per variable frequency converter. A failure rate of the variable speed generator of a known wind turbine is on the order of 4.5%. Consequently, problems related to known wind turbines relate closely to the failure rate of gearboxes, generators, variable frequency converters and associated electronics and inefficiencies of operation.
A solution to the identified problems is to provide a constant rotational velocity as an input to the constant speed electric generator so that the generator in turn can produce a constant frequency output and deliver the power directly to an electric grid. Transmissions have been developed or are under development by the following entities: IQWind, Fallbrook and Voith Wind (Voith Turbo) to provide a constant output from a variable input. U.S. Pat. No. 7,081,689, (the '689 patent) assigned to Voith Turbo of Germany is exemplary of an overall system control design providing three levels of generator control. Voith provides a so-called power split gear and a hydrodynamic Fottinger speed converter or transformer adapted to be connected between a rotor and gear assembly and a synchronous generator for outputting power to a grid, for example, at 50 Hz (European).
Many of the problems of wind turbines are carried forward into run-of-the-river, tidal, ocean and marine hydrokinetic turbines. There is the same problem of having to convert a variable frequency input to a constant frequency output. On the other hand, the density (mass) of water is much greater and its speed is not as variable as wind speed. Generally, for example, rivers flow in one direction and the major ocean currents do the same. Wave generation, however, in oceans and other large bodies of water varies in magnitude with wind and weather. Ocean shore waves are more predictable and a strong undertow can be useful for electric power generation. Tides are reversible and associated turbines may be limited to one direction of water flow.
A concept for improving wind turbines is use of a mechanical direct drive in which a rotor and a shaft drive a generator. Such a direct drive may be used to directly drive an electric generator without using a gearbox, i.e. directly driving the generator. The failure and efficiency problems of gearboxes may be eliminated by eliminating the gearbox with direct drive. One may increase the number of poles by fifty times, use power converters and so result in reduced down time for repairs at the expense of increased cost due to the direct drive assembly. A speed converter to convert variable speed to constant speed is disclosed in priority U.S. Pat. No. 8,388,481 of Kyung Soo Han. The speed converter is entirely mechanical and so improves upon the high failure rate, reliability and efficiency of known electrical/mechanical systems. Speed converters under development are shown in this and other priority patent applications and are referred to as infinitely variable speed converters.
Traction drive infinitely variable transmissions are known produced by Torotrak and Fallbrook. The Fallbrook device may be described by U.S. Pat. No. 8,133,149. A 2004 report, NREL/TP-500-36371, concluded that the Fallbrook device is not scalable. Further speed converters are described by FIGS. 10 and 11 of priority U.S. Pat. No. 8,641,570 of Differential Dynamics Corp. (also known as DDMotion). The DDMotion speed converters are differentiated from those of Torotrak and Fallbrook by their gear drives (no toroids, pulleys or belts) and that they are scalable.
A turbine was produced by Hydrovolts, Inc. The apparatus may comprise a waterwheel and may comprise a gear and belt drive inside which may, because of the belt, be susceptible to slippage. At their web site, a 15 kW waterfall turbine is described for use at a waterfall such as at spillways or outflows in industrial plants. Hydrovolts also produces a 12 kW zero-head canal turbine that allegedly can capture the energy in moving water. Reference may be made to U.S. Published Patent Application 2010/0237626 of Hammer published Sep. 23, 2010, which appears to comprise a waterwheel construction. Hydrovolts' rotating (hinged) blades may control some of the water flow speed, but it is urged that the rotating blades may be susceptible to damage.
A river turbine is known which may be attributed to Free Flow Power Corp. and may have been lowered to the bottom of the Mississippi River or attached to a piling. It is believed that such a device may be very similar to a turbine engine of an airplane but below water level and the water, at velocity, drives a turbine propeller. Due to lowering prices of natural gas, the project became economically unviable (according to their press release in 2012).
It is generally known in the art to utilize devices that look much like wind turbines to capture water energy. A tidal and/or river current turbine is known from FIG. 1 of U.S. Pub. Patent App. 2009/0041584 published Feb. 12, 2009. The diagram provides the labels, showing direction of water flow “A” (from right to left). Note that the turbine rotates on a pole so that rotor blade 150 captures the water as it passes. This device may be available from Verdant Power. It is respectfully submitted that Verdant Power may currently be strengthening their blades and adding pitch control.
A rotating ring device including a rotating ring is known which is available from Oceana Energy Company. FIG. 1 of U.S. Published Patent Application 2012/0211990 of Aug. 23, 2012 of Oceana Energy allegedly comprises hydrofoils both external and internal to the rotating ring.
Perhaps the most like a wind turbine in appearance is the known tidal energy turbine of ScottishPower Renewables, a division of Iberdrola. According to press releases, this tidal device with its propeller (rotor blades) is capable of generating approximately 10 MW of power as an “array” perhaps of twelve or more such devices at less than 1 MW each.
Devices are also known for harnessing the power in water waves such as ocean waves. Such a device is known and available from Pelamis Wave Power. FIG. 1 of Pelamis's U.S. Pub. Patent Application 2013/0239566 of Sep. 19, 2013 shows a Pelamis device 10 floating in the ocean, the device 10 may comprise a plurality of hinged sections 12-A, 12-B, 12-C, 12-D and 12E. The device wiggles and generates power in the direction of a wave from left to right. As the wave passes through the hinged sections, the sections 12A through 12E move up and down with the height of the wave. The wave thus creates movement which may be used to generate electricity. It may be said that the higher the wave, the greater the movement; the calmer the seas, the less the movement.
Most maps of the United States show the major rivers which include the Ohio, the Mississippi, the Missouri, the Snake River and the Pecos and Brazos Rivers of Texas. As can be seen from such a map, there is a great potential to harness the water energy of these rivers in the United States and to power, for example, the entire area covered by the Mississippi River and its tributaries including the Missouri, the Platte and the Red Rivers. Using dams across these rivers to generate electricity would be costly and hinder river traffic. It may be that only Free Flow Power has developed a device for use on such a river as the Mississippi (but Free Flow Power abandoned the Mississippi project in 2012).
Similarly, a map of the world shows the major rivers of the world, further highlighting the potential to harness water energy in rivers world-wide. Also, ocean current maps are shown, for example, showing the Gulfstream. Proximate to the United States, the strong ocean current of the Gulfstream is known to flow northward along the east coast of the United States. On the west coast of the United States, there is known a southward current initiating as the north Pacific drift and, as it passes California, is referred to as the California Coastal current. Other important world currents include and are not limited to the Peru/East Australian current, the Brazilian current/Benguela current, the west wind drift, the West Australian current, the Kuroshio current and the North Atlantic drift. These strong currents are known and have the potential to generate a considerable amount of power but are presently not used for electricity or power generation. (Predictable ocean tides cause water to flow upstream in ocean tributaries at high tide and downstream in ocean tributaries at low tide and may be more widely used for electric power generation.)
A typical hydroelectric power plant is mounted within a dam of a river. A first step in harnessing water energy in this means is to build the dam to create a pressure head that is proportional to the depth of the water backed up by the dam. The backed-up water is represented by a reservoir or lake. At the base of the dam, there may be intake gates which allow water that has been compressed by the head to flow through a penstock to a powerhouse which is one of many such powerhouses that may be constructed along the width of a large dam. One powerhouse may comprise a generator and a turbine which outputs electric power to long distance power lines. Once the water passes through the turbine, it is returned to the river downstream.
A variable torque generator has been described in priority U.S. Pat. Nos. 8,338,481; 8,485,933; and 8,702,552 as well as priority PCT/US2010/042519 published as WO2011/011358. The variable torque generator has one of an axially moveable rotor and stator with respect to its stationary or moveable counterpart stator or rotor so as to vary the amount of overlap by the stator with respect to the rotor from a minimum when the stator is displaced from the rotor to a maximum value when the stator and rotor are proximate to or overlap one another.
In particular, there is described in, for example, WO2011/011358 or U.S. Pat. No. 8,338,481 (the U.S. '481 patent), the concept of measuring torque/rpm on an output shaft of a system such as a wind or river/tidal/ocean wave/ocean current turbine (which may be referred to herein as a marine hydrokinetic (MHK) turbine) for providing a constant output from a variable flow input. The measured torque/rpm value may be compared with a torque/rpm value stored in a memory and, if the measured torque/rpm is high in comparison, then, the moveable rotor or stator of a variable torque generator may be moved axially to a position more in keeping with the high measured torque/rpm value, i.e. such that the stator is moved away from the rotor axially under motor control through a feedback loop. When the measured torque/rpm is low in comparison with an expected value, the moveable rotor or stator may be moved axially toward one another to match a low value of torque/rpm so that the speed of the output shaft may increase and vice versa. This variable torque generator process continues so as to maintain a relationship between speed of input (such as wind or river/tide/ocean wave/ocean current) to match a desired rotational speed of output shaft and to maintain output shaft speed, for example, if used as an electric power generator, to produce 60 Hz U.S. electric frequency or in Europe 50 Hz European frequency electric power.
In either the priority '481 U.S. patent or the WO 2011/011358 printed publication priority documents, FIG. 8 shows the concept of an infinitely variable torque generator, meaning that the one of the moveable rotor or the stator may be moved, for example, by a servo motor, not shown, to any position of proximity to or distance from one another or such that their respective magnetic flux fields are located far away from one another so as to not couple with one another or to couple with one another, for example, to have an effect to cause a coupling of rotor and stator and a magnetic force field tending to cause the rotor to be stationary with the stator or move with the stator. In FIG. 10, the rotor and stator of the variable torque generator are shown such that the rotor 810 is directly coupled to the shaft 820. “When the stator parts 830(a) and 830(b) are moved away from rotor 810, a minimum input torque results. The operation of a control may be as follows via measuring a torque value stored in memory proximate to the maximum torque that a given rotor shaft 820 may receive (a maximum allowable torque value), the stator parts 830(a) and 830(b) may be moved by a motor (not shown) to be in removed torque position or a position in between maximum and minimum torque positions whereby a close-to-maximum torque position may be achieved in relation to the measured torque and the maximum allowable torque(/rpm) value or value stored in memory.”
There remains a need in the art to provide applications of such a variable torque/power generator assembly as well as a spur/helical gear assembly (Transgear™ gear assembly) in connection with the generation of electrical energy/power (variable power generator, VPG) from renewable sources such as wind and river/tide/ocean wave/ocean current, that is, a marine hydrokinetic turbine electric power generator among other possible applications in wind turbines for generating electric power at constant alternating current frequency for a power grid.